/**
*      author: Y_Yao
*      created: 2024-11-22 20:08:04
**/

#include<bits/stdc++.h>

using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;

void solve()
{
    string s;
    cin >> s;
    int n = s.size();
    string t = " ";
    s = t + s;
    if(n % 2 == 1)
    {
        cout << "No" << endl;
        return;
    }

    map<char,int> hash;
    for(int i = 1;i <= n;i++)
    {
        hash[s[i]]++;
        if(i <= n / 2 && s[2 * i - 1] != s[2 * i])
        {
            cout << " No" << endl;
            return;
        }
    }

    for(auto e : hash)
    {
        if(e.second != 2)
        {
            cout << "No" << endl;
            return;
        }
    }

    cout << "Yes" << endl;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}